The northeastern Atlantic species Mycale micracanthoxea Buizer & Van Soest, 1977 is a component of subtidal shallow water and brackishwater harbour poles and pontoons from The Netherlands, where it grows attached to shells, barnacles, etc. It was found in similar zones and habitats of Algeciras Bay (Gibraltar Strait, southern Spain) and Isla Cristina (Huelva, southern Spain) where it is very common. This new record constitutes the southernmost limit of the geographical range of this species. This article presents some data on the anatomical variability of Mycale micracanthoxea, along with a discussion on the possible causes of its observed distribution.